1. Field of the Invention
The invention relates to a directional control valve comprising a valve body guided in a housing, via which a front-side connector can be connected with a radial connector.
2. Description of the Related Art
Continuously adjustable directional control valves are, for instance, used as proportionally adjustable throttles. The directional control valve can be flown through in two directions, i.e. from the front-side connector to the radial connector and—in the opposite direction—from the radial connector to the front-side connector. The valve body may, for instance, be designed as a cup-shaped valve shift with radial openings being formed in the casing thereof, via which the radial connector can be opened or closed. The actuation of the valve is preferably performed by means of a proportionally adjustable electromagnet via the plunger of which the valve body can be shifted against the force of a compression spring. In order to minimize the actuating forces, the pressure acting on the front side of the valve body is guided into a rearward pressure chamber via a connecting bore, so that the valve body is substantially pressure-balanced.
In FIG. 11, which is referred to as early as now, the volumetric flow characteristic of such a two-two directional control valve is illustrated, with the stroke performed by the valve body being illustrated in relation to the relative input voltage of the electromagnet, i.e. to the input voltage in relation to the maximum voltage. The different performance curves characterize the volumetric characteristics for various pressure differences Δp, wherein the flattest performance curve represents a small pressure difference while the performance curves become steeper with increasing pressure difference Δp. According to FIG. 11, the right, flat performance curve corresponds to a stable, ideal course, such as it ensues as a rule with a through-flowing from the front-side connector to the radial connector or—in the case of through-flowing in the opposite direction—with low pressure differences. In the case of higher pressure differences and volume flows (left performance curve in FIG. 11), abrupt bursting of the valve body may occur. This abrupt bursting is shown by the step in the left performance curve of FIG. 11, according to which the stroke increases sharply with constant input voltage. Furthermore, it may be taken from FIG. 11 that instabilities, which are shown by the oscillations in the performance curve, may occur when through-flowing from the radial connector to the front-side connector takes place at high volume flows.
The afore described instabilities, i.e. the abrupt bursting of the valve body and the oscillations in the end portion of the stroke, result from the flowing forces acting upon the valve body in the case of high volume flows, which act on the valve piston such that the actual throttle cross-section does not correspond to the value that is at that moment predetermined by the input voltage in the case of ideal conditions. It is of particular disadvantage that the performance curves with valves of the volumetric flow characteristic illustrated in FIG. 10 differ for the two through-flow directions, i.e. the through-flowing from the front-side connector to the radial connector and in opposite direction, so that the consumers cannot be triggered in the predetermined manner.